Super tuning car runs good shooting for great

When you have a rowdy cam with lots of overlap and low vacuum at idle, you're starting from a decidedly different point than your average '60's-'70's pass. car tune. Your initial timing is usually much higher than the limp-wristed factory settings. Start adding extra timing in and you can see why it doesn't work in some situations.

Trying to tune vacuum advance so it doesn't produce negative effects seems counterproductive. If you have to fiddle with it more than just a little bit, it's not worth the effort.

An air fuel ratio gauge is a great tool but it's only for one part of the equation. It's easy enough to run a vacuum gauge into the car while driving and see what numbers come up during different driving scenarios. Make a chart and try to determine where and how the extra advance would do benefit the tune in specific situations. I bet you wouldn't find many places it would be of use except for part throttle cruise on the highway.